Advanced Electronic Signature (AES), Simple (SES) and Qualified (QES): the 3 eIDAS Levels

The advanced electronic signature (AES) is the most widely used level in B2B and the only one to offer a legal presumption of integrity without imposing a smart card on the signer. Alongside the simple signature (SES) and the qualified signature (QES), it comprises the three levels defined by the European eIDAS Regulation. Here is how to choose the right level according to the nature of your document, its expected probative value and the acceptable friction for the signer.

What is an Advanced Electronic Signature (AES)?

The advanced electronic signature is the intermediate level defined by Article 26 of the eIDAS Regulation. It must meet four cumulative conditions: (1) be uniquely linked to the signer, (2) allow identification of the signer, (3) be created using data under the signer's exclusive control, (4) allow detection of any subsequent modification of the signed document. In practice, these conditions are met through strong authentication (email + OTP SMS), a time-stamped audit trail and cryptographic hashing of the PDF.

The AES benefits from a legal presumption of integrity and origin which reverses the burden of proof before the judge: it is up to the person who contests the signature to prove its falsity, not for the signer to prove its validity. This is what fundamentally distinguishes AES from SES, where reliability is assessed on a case-by-case basis by the judge.

The Three Levels Defined by eIDAS

The European Regulation eIDAS (no. 910/2014) organises electronic signatures into three levels, corresponding to increasing degrees of requirement in terms of signer identification and proof robustness. Understanding these levels clearly enables you to choose the signature appropriate for each document, without over-sizing the process.

Level 1: Simple Electronic Signature (SES)

The simple electronic signature is the basic level. It corresponds to any manifestation of electronic consent: a click on "I accept", a checkbox, an initial drawn on a touchscreen.

• Requirements: clear consent, minimal identification (email)

• Proof: weak to moderate, varies according to the service provider

• Use cases: quotation, purchase order, internal agreements, general terms and conditions

• Signer friction: virtually none — the signer does not create an account

The SES is sufficient for the vast majority of current commercial exchanges where the risk of dispute is low. It remains legally valid, with the judge assessing on a case-by-case basis the reliability of the process.

Level 2: Advanced Electronic Signature (AES)

The advanced signature strengthens signer identification and establishes a unique link between the signer and the document. It rests on four criteria set out in Article 26 of eIDAS:

• it is linked to the signer in a unique manner

• it allows identification of the signer

• it is created using means which the signer keeps under their exclusive control

• it is linked to the document in a way that allows detection of any subsequent modification

In practice, AES relies on two-factor authentication: unique link sent by email + OTP code received by SMS. The final PDF incorporates a time stamp and a detailed audit trail.

• Use cases: employment contract, lease, mandate, commercial contract with significant stakes, NDA

• Signer friction: low — an SMS code to enter in addition to email

• Proof: strong, rebuttable presumption of validity

Level 3: Qualified Electronic Signature (QES)

The qualified signature is the highest level. It relies on a qualified certificate issued by a qualified trust service provider (QTSP) listed on the trust list of an EU Member State, and on a secure signature creation device (e.g. YubiKey, smart card).

• Legal value: equivalent to a handwritten signature throughout the EU

• Use cases: authentic deeds, public procurement, certain notarial acts

• Signer friction: high — identity verification face-to-face or via video KYC

• Cost: significantly higher than SES/AES

For most companies, QES is rarely necessary on a daily basis. It becomes essential when the law requires it (legal proceedings, certain public procurement) or when the contract has exceptional value.

Quick Comparison Table

Criterion | Simple | Advanced | Qualified

Identification | Email | Email + OTP SMS | Qualified certificate + identity verification

Legal value | Proof to be assessed | Presumption of validity | Equivalent to EU handwritten signature

Friction | Virtually none | Low | High

Typical use case | Quotation, purchase order | Employment contract, lease | Notarial deeds, public procurement

Cost | Low | Moderate | High

How to Choose the Right Level

The simple rule: align the level with the stakes of the document.

• If the document is contested, what is at stake? A few hundred pounds or a contract worth several tens of thousands?

• Is the relationship with the signer known (long-standing customer) or unknown (first contact)?

• Does the document fall under a legal framework that imposes a specific level (e.g. employment contract, lease)?

As a general rule: SES for simple agreements, AES for anything involving HR, real estate, finance; QES only when the law requires it.

Common Mistakes

• Systematically taking QES "to be safe": unnecessary friction for the signer, high cost, often over-sized.

• Settling for SES for everything: in the event of a dispute over an employment contract, the absence of strong authentication can weaken the proof.

• Confusing validation and signature: a delivery confirmation is not a signature.

How Certyneo Helps You

Certyneo natively supports simple (SES) and advanced (AES) levels, with dual OTP email + SMS via Twilio Verify for AES. For cases requiring QES, Certyneo interfaces with several qualified European service providers (Docaposte Certigna, Universign, CertEurope) to trigger qualified signature without changing tools.

You can define the signature level document by document according to the stakes — or by template if you have industrialised a process.

Discover the Certyneo electronic signature solution

FAQ

Can I mix levels in the same envelope?

Yes. A multi-document envelope can include a quotation signed with SES and a contract signed with AES, for example. Each signer sees the authentication adapted to the document they must sign.

Is advanced signature recognised internationally?

Within the EU yes, under the principle of mutual recognition of eIDAS. Outside the EU, recognition depends on the local legal framework — to be checked according to the jurisdiction concerned.

Do I need a personal certificate to sign with AES?

No. AES can be obtained without a prior personal certificate thanks to dual OTP. This is what makes AES very accessible, whereas QES requires a qualified certificate.

Is qualified signature mandatory for an employment contract?

No. The employment contract accepts advanced signature (AES), which already offers strong presumption of validity. For more details, see electronic signature of employment contract.

How do I verify the level of a signed document?

Open the PDF in Adobe Acrobat Reader: the signature properties display the level, the signer and the time stamp. You can also use an online verifier.

Conclusion

Choosing the right level of electronic signature is about finding the balance between probative value and friction for the signer. Start simple, move up a notch when the legal stakes require it.

Try Certyneo to send, sign and track your documents online simply, quickly and securely.